The present invention is related in general to the field of semiconductor devices and assembly and more specifically to the design and fabrication of a plastic header adaptable to through-hole as well as surface mount board assembly.
For many electronic applications, it is advantageous from electrical and cost standpoints to first group a plurality of electronic components together and to assemble this group on an intermediate substrate (xe2x80x9ccomponents boardxe2x80x9d). In a second step, this subassembly unit is then assembled on the actual circuit board or motherboard. Examples can be found in applications as diverse as power supplies, telephone stations, central offices, desktop computers, automotive equipment, and many more.
In conventional technology, the substrates preferred for assembling the components group are metallic leadframes. These leadframes have to be custom-made for each size and input/output configuration of the subassembly units. Unfortunately, these leadframes are expensive, since their manufacture requires costly stamping tools for stamping the leadframes from the original metal sheets. (The alternative method of etching the leadframes is usually even more expensive).
In addition, one has to decide beforehand, whether the leadframes should be designed and employed for through-hole assembly onto circuit boards, or for surface mounting. An individual leadframe cannot be converted from one to the other assembly method. This fact puts severe constraints onto the design and assembly process of circuit boards.
Furthermore, in today""s technology, the process of assembling the components onto the leadframes has to be performed one unit at a time, since it does not lend itself to batch processing; the process is, therefore, not cost-effective and also requires intensive process and quality controls.
In summary, an urgent need has arisen for a coherent concept of a components substrate which is low-cost in its structure and fabrication, reliable in its performance, and flexible in its method of usage. The substrate design, method of fabrication and method of usage should be flexible enough to be applied for different semiconductor product families and a wide spectrum of design and assembly variations, and should achieve improvements towards the goal of enhanced process yield and device reliability. Preferably, these innovations should be accomplished while shortening production cycle time and increasing throughput, and using the installed equipment base in the user""s house so that no investment in new assembly pick-and-place machines is needed.
According to the present invention, a low-cost header for connecting an electronic components board to a circuit board is disclosed, consisting of side walls made of an unwarpable plastic material and joined together to form a frame around an area substantially the same as the area of the components board. A plurality of metal pins are located in the frame, each having one end extending from said frame such that these ends can be soldered to the components board concurrently with the solder attachment of the components to the board. The other ends of the pins can be formed so that they are adjusted for either through-hole attachment to circuit boards, or for surface mounting.
It is an aspect of the present invention to be applicable to semiconductor devices used for a variety of different applications, for instance DC to DC converters, power supplies, telephone central stations, telecommunication equipment, transmitting towers, central office computers. In all applications, the invention achieves technical advantages as well as significant cost reduction and production throughput increase.
It is another aspect of the present invention to maintain for the plastic header the same footprint, which the conventional metallic leadframe uses. Consequently, there is no change required for the circuit board of the end-user.
It is another aspect of the present invention to design and employ a tab for the plastic header such that the attachment of the header to the components board is facilitated and can be performed by conventional pick-and-place machines. Further, the tab can be designed so that is provides orientation control for the automatic machinery, and can be removed and discarded after handling by the machines.
It is another aspect of the invention to eliminate separate solder reflow steps for attaching the semiconductor components to the components board and for attaching the header to the components board. The two solder attachment operations can now be performed concurrently, thus lowering the manufacturing cost and enhancing product reliability.
It is another aspect of the invention to provide header material and designs, and assembly processes, for batch processing. As an example, instead of only one unit at a time, header panels of more than a dozen units can be processed.
It is another aspect of the invention to select plastic materials for the header which are insensitive to deformation in the temperature range of the solder process. Consequently, the headers do not warp in the process temperature range. Further, they are tolerant to process-induced stresses in the practical thickness ranges.
These aspects have been achieved by the teachings of the invention concerning materials, structure and methods suitable for mass production. In one embodiment of the invention, nylon-based materials such as flame retardant, heat stabilized and glass-fiber strengthened Stanyl(copyright) are employed, varying the header wall thickness as parameter.
In another embodiment of the invention, geometrical header dimensions and pin locations are provided to serve as examples for assembling the components for a DC to DC converter, as manufactured by Power Trends, Warrenville, Ill., U.S.A.
The technical advances represented by the invention, as well as the aspects thereof, will become apparent from the following description of the preferred embodiments of the invention, when considered in conjunction with the accompanying drawings and the novel features set forth in the appended claims.